Image processing apparatus and method thereof for adding a predetermined pattern to an image

ABSTRACT

An image processor in which information or a pattern is added to input image data, with the added information or pattern having a resolution or density which is different from that of the input image data.

This application is a division of application Ser. No. 08/125,831 filedSep. 24, 1993, now U.S. Pat. No. 5,557,416.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to an image processing apparatus and method and,more particularly to a color image processing apparatus and method whichis helpful in guarding against the production of counterfeiting of banknotes, securities, and the like.

Conventionally, various techniques are implemented in a color imageprocessing apparatus, such as a full-color copying machine, in order toprevent the counterfeiting of bank notes and securities. One techniqueis such that a pattern, which is unique to each image formationapparatus but imperceptible to human eyes, is added on the imageinformation at a predetermined modulation amount in order to identifythe image processing apparatus used for counterfeiting. Such techniqueis disclosed in U.S. Pat. No. 5,257,119, U.S. Pat. No. 5,457,540, andU.S. Ser. No. 08/009,735. In a case where bank notes or securities havebeen forged by such color image formation apparatus, if a unique patternis read and identified by a reading apparatus capable of detecting apredetermined wavelength range represented by the color printed on acounterfeit, the image formation apparatus used for the counterfeitingcan be identified. Thus a counterfeiter can affectively be traced.

In the conventional technique, a pattern is added in a neutral tint sothat the pattern itself cannot be read; however, fog appears on an imagebecause the pattern exists on the image boundary where an image beginson a printing paper. Particularly, the problem is evident in a boundarybetween an image portion and a non-image portion, such that an add-onpattern stands out resulting in the deterioration of image quality.

Furthermore, when the image formation characteristic of the color imageformation apparatus is changed, the add-on unique pattern cannot be readand/or the image may not be formed properly. That is, the added uniquepattern may not be able to be read since the change of characteristicsare not reflected in the image density at a highlight portion of theimage (in a low density range). This is due to the dependency on thetone characteristic of the color image formation apparatus. In contrast,in the density range where the contrast is strong, the add-on uniquepattern becomes visable (visible).

More particularly, in an electrophotographic process copying machine,when an image density reproduction capability decreases by deteriorationof a photoreceptor and the image density cannot be fully expressed, adrawback occurs in that an add-on unique pattern cannot be reproducedand read as a difference of the image densities.

When the image density reproduction capability increases and the imagedensity is excessively expressed, the drawback is such that the add-onunique pattern becomes visable because the difference between the imagedensity of the add-on unique pattern and that of the original image issignificantly large; thus the image is not accurately reproduced.

Furthermore, when a recording density of the fullcolor copying machineis increased to duplicate specific originals such as bank notes, stamps,securities, and postage stamps, since the color reproduction isdeteriorated and character lines are emphasized, the drawback occurs inthat the unique pattern of the image formation apparatus is difficult toreproduce. In the low density range in particular, the unique pattern isdifficult to reproduce and read. In contrast, in the intermediatedensity range, the added unique pattern becomes visable.

SUMMARY OF THE INVENTION

The invention is directed to an image processing apparatus and method inwhich information or a pattern is added to input image data, with theadded information or pattern having a resolution or density which isdifferent from that of the input data. The input image data may includea plurality of color component image date representing a color image.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated and constitute a partof the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a side view illustrating the construction of a full-colorcopying machine which is a typical embodiment of the present invention;

FIG. 2 is a block diagram illustrating the construction of an imagescanner 201 of the full-color copying machine shown in FIG. 1 accordingto a first embodiment;

FIG. 3 is a block diagram illustrating the construction of adetermination circuit 409;

FIG. 4 is a circuit diagram illustrating the construction of athinning-out circuit 301;

FIG. 5 is a circuit diagram illustrating the construction Of a dividingcircuit 310;

FIG. 6 is a timing chart of a control signal in a main scanningdirection;

FIG. 7 is a block diagram illustrating the construction of an integrator306;

FIG. 8 is a diagram illustrating an input signal of the integrator 306;

FIG. 9 is a diagram illustrating an output signal of the integrator 306;

FIG. 10 is a block diagram illustrating the construction of a comparatormodule 310;

FIG. 11 is a block diagram illustrating the construction of a patternaddition circuit 410;

FIG. 12 is a top view of an original glass table (platen) 203;

FIG. 13 is a flowchart for explaining a service mode;

FIG. 14 is a diagram illustrating an example of the result ofduplication;

FIG. 15 is a flowchart for explaining the procedure for setting apattern level selection signal PS;

FIG. 16 is a diagram illustrating the relationship between a signal CNOand a print output;

FIG. 17 is a side view illustrating the construction of main portions ofthe full-color copying machine in accordance with a second embodiment;

FIG. 18 is a block diagram illustrating the construction of a controlcircuit 2107 shown in FIG. 17 which controls a modulation amount of aserial-number pattern added using an ITOP signal as an input;

FIG. 19 is a diagram illustrating a state where a serial-number patternis added to the density signal of an output image;

FIG. 20 is a diagram illustrating an example of the serial-numberpattern;

FIG. 21 is a diagram illustrating the relationship between an imagesignal for adding the serial-number pattern and a position where theserial-number pattern is added on a recording paper;

FIG. 22 is a diagram illustrating another example of the relationshipbetween an image signal for adding the serial-number pattern and aposition where the serial-number pattern is added on a recording paper;

FIG. 23 is a block diagram illustrating the construction of a circuitwhich controls a modulation amount of the serial-number pattern which isadded using a BD signal as an input;

FIG. 24 is a diagram illustrating an example where the right and leftedges of the recording paper are detected in accordance with the BDsignal, and then the modulation amount is set;

FIG. 25 is a diagram illustrating the arrangement of the BD detector2114;

FIG. 26 is a block diagram illustrating the construction of the circuitwhich controls the modulation amount of the serial-number pattern addedusing the ITOP signal and BD signal as inputs;

FIG. 27 is a sectional view illustrating the construction of mainportions of the full-color copying machine in accordance with a thirdembodiment;

FIG. 28 is a flowchart for explaining the recording operation inaccordance with the third embodiment;

FIG. 29 is a four-quadrant chart illustrating the state where the tonein a character mode is reproduced;

FIG. 30 is a four-quadrant chart illustrating the state where the tonein a photo mode is reproduced;

FIG. 31 is a four-quadrant chart illustrating the tone reproductioncharacteristic of yellow in the character mode;

FIG. 32 is a diagram illustrating an example of developing a biaswaveform;

FIG. 33 is a diagram illustrating the tone characteristics of the outputimage when the developing bias shown in FIG. 32 is applied;

FIG. 34 is a diagram illustrating another example of the developing biaswaveform;

FIG. 35 is a diagram illustrating the tone characteristics of the outputimage when the developing bias shown in FIG. 34 is applied;

FIG. 36 is a diagram illustrating a surface electric potential of aphotosensitive drum 2004;

FIG. 37 is a diagram illustrating the tone characteristics of the outputimage of M, C, BK components;

FIG. 38 is a diagram illustrating the tone characteristics of the outputimage of Y component;

FIG. 39 is a block diagram illustrating the construction of the imagescanner 201 in accordance with a fourth embodiment;

FIG. 40 is a diagram for describing an adding pattern;

FIG. 41 is a diagram illustrating the construction relating to the mainscanning direction of an add-on line;

FIG. 42 is a diagram illustrating the construction relating to thesub-scanning direction of an add-on line;

FIGS. 43, 44A, and 44B are diagrams illustrating the informationrepresentation by the add-on line;

FIGS. 45, 46, and 47 are block diagrams illustrating the construction ofa pattern addition circuit 410;

FIG. 48 is a diagram illustrating an example of the result ofduplication;

FIG. 49 is a block diagram illustrating the construction cf a modifiedexample of the image scanner 201 in accordance with the fourthembodiment;

FIG. 50 is a block diagram illustrating another construction of thepattern addition circuit 410;

FIG. 51 is a flowchart illustrating the procedure 5 for forming a colorimage in accordance with a fifth embodiment;

FIG. 52 is a diagram illustrating the relationship between the densityvalue of a serial-number pattern and the density value of an outputimage;

FIG. 53 is a four-quadrant chart showing the tone characteristicsconversion;

FIGS. 54A and 54B are diagrams illustrating the modulation pattern andmodulation characteristic;

FIGS. 55A and 55B are diagrams illustrating another example of themodulation pattern and modulation characteristic; and

FIGS. 56A and 56B are diagrams illustrating another example of themodulation pattern and modulation characteristic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

In the embodiment, an electrophotographic process type of full-colorcopying machine is used-as a typical image processing apparatus.However, the present invention is applicable to a silver-halide process,a thermal transfer process, and a sublimation type process of the imageprocessing apparatus.

First Embodiments

General Description of Apparatus (FIG. 1)!

FIG. 1 is a sectional view showing the internal construction of acopying machine according to a first embodiment of the presentinvention. In FIG. 1, numeral 201 denotes an image scanner for readingan original image at a resolution of 400 dpi (dot/inch) and performingdigital signal processing. Numeral 202 designates a printer for printingan image, which corresponds to the original image read by the scanner201, on paper in full color at the resolution of 400 dpi.

The image scanner 201 includes a pressure plate 200 having a mirrorsurface. An original image 204 on an original glass table (platen) 203is irradiated by means of lamps 205. An image is formed on a three-linesensor (hereinafter referred to as a "CCD") 210 of the colors red (R),green (G) and blue (B) via mirrors 206, 207, 208 and a lens 209, and theimage is sent to a signal processor 211 as red (R), green (G) and blue(B) components of full-color information. The entire surface of theoriginal image is scanned (subordinate scanning) by mechanically movingthe lamps 205 and mirror 206 at a velocity v as well as the mirrors 207,208 at a velocity 1/2 v in a direction perpendicular to the electricalscanning direction (main-scanning direction) of the COD 210.

The signal processor 211 electrically processes the read image signal,separates the signal into magenta (M), cyan (C), yellow (Y) and black(BK) components and sends these components to the printing unit 202. Atleast one component among the M, C, Y, BK components is sent to theprinter 202 per scan of the original image in the image scanner 201, anda single print-out is completed by a total of four scans of the originalimage.

The M, C, Y, BK image signals received from the image scanner 201 aresent to a laser driver 212. The laser driver 212 modulates and drives asemiconductor laser 213 in dependence upon the particular image signalsent. The laser beam is made to scan across a photosensitive drum 217via a polygon mirror 214, an f 4 lens 215 and a mirror 216. Numeral 218denotes a revolving developer comprising a magenta developing unit 219,a cyan developing unit 220, a yellow developing unit 221 and a blackdeveloping unit 222. These four developers come into alternate contactwith the photosensitive drum 217 so that an electrostatic latent imageformed on the photosensitive drum 217 is developed by means of toners.Numeral 223 denotes a transfer drum upon which paper fed from a papercassette 224 or 225 is wound so that the image developed on thephotosensitive drum 217 may be transferred to the paper.

After the four colors M, C, Y, BK have been thus transferredsuccessively, the paper is passed through a fixing unit 226 to fix thetoners on the paper, after which the paper is ejected.

Image Scanner (FIG. 2)!

FIG. 2 is-a block diagram showing the construction of an image scanner201. Numerals 210-1, 210-2, 210-3 in FIG. 2 denote CCD (Charge CoupledDevice) line sensors having spectral sensitivity characteristics for red(R), green (G) and blue (B), respectively. The output signal of eachline sensor is subjected to an A/D conversion, after which it is outputas an 8-bit signal. Accordingly, each of the R, G, B components isrepresented by 0-255 levels in accordance with the brightness.

The CCD line sensors 210-1, 210-2, 210-3 used in the present embodimentare arranged so as to be spaced apart at a predetermined distance, andtherefore a space displacement is corrected using delay elements 401 and402.

Numerals 403, 404, 405 are log converters constituted by a look-up tableROM or RAM for converting a brightness signal into a density signal.Numeral 406 denotes a well-known masking-UCR (Under Color Removal)circuit. In the masking-UCR circuit 406, each of the magenta (M), cyan(C), yellow (Y) and black (BK) signals for image formation are generatedat a prescribed bit length (e.g., eight bits) in frame-sequentialfashion, based upon the RGB signals input thereto, whenever there is areading operation.

Numeral 407 denotes a well-known space filter circuit which corrects thespace-frequency characteristic of the output signal from the circuit406. Numeral 408 denotes a density conversion circuit for correcting theoutput signal in conformity with the density characteristic processed bythe printer 202. Like the log converters 403-405, this circuit isconstituted by a ROM or RAM.

Numeral 414 denotes a microcomputer (hereinafter referred to as a "CPU")for supervising control of the apparatus. Numeral 415 denotes a ROMwhich stores a program for operating the CPU 414, and numeral 416denotes a RAM used as a work area which executes various programs.Numeral 413 denotes an input/output port (hereinafter referred to as an"I/O port") connected to the CPU 414 and numeral 409 denotes adetermination circuit which determines a specific original.

The determination circuit 409 determines a possibility that the originalplaced on the original glass table 203 is at least one of a plurality ofspecific originals (documents that should not be copied). Thedetermination signal H is output in two bits. If there is a strongpossibility that the original is one of the specific originals, H="3" isoutput. On the other hand, if the possibility is rare, H="0" is output.The determination circuit 409 further comprises a thinning-out circuit301 which performs a thinning-out processing of the input signals R, G,B and a frequency dividing circuit 310, which are described later withreference to FIG. 3.

A signal CNO is a two-bit control signal which indicates each color ofthe image, which is formed by the four reading operations (scanningoperations) with respect to four output colors M, C, Y, and BK for eachcolor image. FIG. 16 shows the relationship between the signal CNO andthe print output. The signal CNO is generated by the CPU 414 through theI/O port 413 to change conditions for the operation of the masking/UCRcircuit 406. The signal CNO is also input to the determination circuit409 to change the criteria with respect to the four reading operationsand thus determination on a different specific original can beperformed.

Numeral 410 denotes a pattern addition circuit at which a pattern whichcannot be visually discriminated is added to a duplicate imagecorresponding to a 2 bit pattern level selection signal PS designed bythe CPU 414. The pattern to be added is generated from the image signalP read by the image scanner 201.

Determination Circuit (FIGS. 3-5)!

FIG. 3 is a block diagram of the construction of the determinationcircuit 409. The thinning-out circuit 301 shown in FIG. 3 thins out datato reduce the processing load of the determination circuit 409. Numeral302 denotes a color-matching look-up table ROM (hereinafter referred toas a "LUT") which performs the color matching on a plurality of specificoriginals (securities, bank notes, etc.) and input data. The LUT 302investigates color distribution with regard to 32 specific originals inadvance and holds the results of judgment such as the bit informationwhen the color of a pertinent pixel coincides with a color of thespecific original and when the color does not coincide with the color ofthe specific original. The 32 specific originals are the total in thecase where the judgment of eight types of specific originals arerespectively assigned to four scanning operations for M, C, Y, and BK.

In the LUT 302, the signal CNO is input to the two higher address bits(A16, A15), and five higher bits of the thinned-out image signal of eachof the colors R, G, B are input to the 15 lower address bits (A14-A0)which are thinned out by the thinning-out circuit 301. The operation ofthe thinning-out circuit 301 will be described later. In each of thesignal CNO values 0 to 3, whether the color tone of the pertinent pixelcoincides with the color tone of the 8 specific originals issimultaneously output in correspondence with the 8-bit data. That is, ifall of the color tones coincide, all bit values of D7-D0 become "1". Onthe other hand, if none of the color tones coincide, all bit valuesbecome "0". Furthermore, if one of the color tones is coincided with theinput image signal, the bit value corresponding to that particularsignal (one of D7-D0) becomes "1". Accordingly, a determination is madewith respect to the 32 specific originals by four cycles of readscanning.

Numerals 303-1, 303-2, . . . 303-8 (See FIG. 3) denote a color tonedetermination circuit constituted of the same hardware. Each circuitcomprises an integrator 306, registers 307-1, 307-2, 307-3 and acomparator module 308 determines a possibility of the existence of aspecific original in the read originals, and outputs a 2-bitdetermination signal. Numeral 309 denotes a maximum value circuit whichoutputs a maximum value among the determination results output from thecolor tone determination circuits 303-1, 303-2, . . . 303-8 as a 2-bitdetermination signal. That is, the determination result corresponding toone of the 8 specific originals which is the most probable to exist isoutput.

The detail of the construction of the thinning-out circuit 301 andfrequency dividing circuit 310 shown in FIG. 3 is described below.

FIG. 4 is a block diagram of the construction of the thinning-outcircuit 310, and FIG. 5 is a block diagram of the construction of thefrequency dividing circuit 310. In FIG. 4, numerals 455-457 and 461-466are flip flops, and numerals 458-460 are selectors. In FIG. 5, numerals451 and 453 are inverters, numeral 452 is a 2-bit counter, and numeral454 is an AND gate.

The flip flops 455, 456, 457, 461, 462, 463 and the selectors 458, 459,460 hold data at the timing of the clock CLK while the flip flops 464,465, and 466 hold data at the timing of the clock CLK'.

In FIG. 4, the 5 higher address bits of the output of the flip flop 462are input to the flip flop 464 and output as an R' signal. Similarly,the 5 higher address bits of the output of the flip flop 462 are inputto the flip flop 465 and output as a G' signal. Similarly, the 5 higheraddress bits of the output of the flip flop 466 are input to the flipflop 463 and output as a B' signal.

In the frequency dividing circuit 310, the two-bit counter 452 iscleared (initialized) by the signal HSYNC which is the main scanningsynchronizing signal, counts the CLK thereafter, and outpuGs the countvalue in 2 bits (D0, D1). The upper bit D1 of these count values isoutput as CLK', and a logical product of an inverted signal of the lowerbit D0 and the upper bit D1 is output as an SEL signal.

Timing Chart (FIG. 6)!

FIG. 6 is a timing chart of control signals with respect to the mainscanning direction in accordance with the embodiment.

VSYNC signal is a sub-scanning interval signal which indicates an imageoutput interval in the subscanning direction. A HSYNC signal is a mainscanning synchronizing signal for synchronizing the start of the mainscanning. CLK represents an image transfer clock which is a master clockfor Various image processings in the first embodiment.

On the other hand, CLK' represents a clock which is obtained by dividingthe frequency of the CLK by 4 to be used as a master clock for thedetermination circuit 409. A SEL signal is a timing signal for use inthe thinning-out circuit 301. The CLK' clock and SEL signal aregenerated by the frequency dividing circuit 310 shown in FIG. 5.

As a consequence, in the thinning-out circuit 301, the signal R (G, orB) transferred at CLK is thinned out at a rate of 1/4 and issynchronized with CLK' to obtain a signal R' (G', or B') as shown inFIG. 6. As described above, since the information amount is reduced tothe 5 higher bits of each of the signals RGB, each of the signals RGBbecomes 5-bit signal.

Integrator (FIGS. 7-9)!

FIG. 7 is a block diagram showing the construction of the integrator 306according to the embodiment, and FIGS. 8 and 9 are diagrams showing theinput and output of the integrator 306 according to the embodiment.

In FIG. 7, numerals 501, 505 denote flip-flops which hold data at thetiming of the leading edge of the CLK' signal. Numeral 502 denotes amultiplier to which two 8-bit signals (A, B) are input. The multiplier502 multiplies these signals together and outputs an 8-bit signal(A×B/255) as the result. Numeral 503 denotes a multiplier to which a1-bit input signal (C) and an 8-bit input signal (D) are input. Themultiplier 503 multiplies these signals together and outputs an 8-bitsignal (C×D) as the result. Numeral 504 denotes an adder to which two8-bit signals (E=A×B/255, F=C×D) are input. The adder 504 adds thesesignals together and outputs an 8-bit signal y_(i) (=E+F) as the result.

Accordingly, in the integrator of this embodiment, an 8-bit outputsignal y_(i) is expressed by the following equation when a binary inputsignal x_(i) is applied thereto:

    y.sub.i =(α/255)·y.sub.i -1+β·x.sub.i-1 (1)

where α and β represent constants that have been preset. The variouscharacteristics of the integrator are decided by the size of thesevalues.

For example, in a case where α=247, β=8 holds, an output y_(i) of thekind shown in FIG. 9 is produced in response to an input x_(i-1) of thekind shown in FIG. 8.

An input "1" regardless of the fact that values on either side thereofare almost "0", as at points 701, 702, and an input "0" regardless ofthe fact that values on either side thereof are almost "1", as at point703, may be considered to be noise. This is processed by the integrator.Specifically, appropriate threshold values such as R1, R2, R3 are setrespectively in the registers 307-1˜307-3 of FIG. 3, and the outputy_(i) of the integrator is binarized based upon these threshold values,whereby the noise is removed.

Comparator Module (FIG. 10)!

FIG. 10 is a block diagram of the construction of the comparator module308 according to the first embodiment. In FIG. 10, numerals 801, 802,and 803 denote comparators, numeral 804 denotes an inverter, numeral 805denotes an AND gate, and numerals 806 and 807 denote OR gates.

As described earlier for the explanation of the integrator 306,threshold values R1, R2, and R3 mentioned above with reference to FIG. 9are previously set in the registers 307-1, 307-2, and 307-3,respectively. The relation such as R1>R2>R3 is then established.Accordingly, the determination result is quantized into 2 bits andoutput. That is:

OUTPUT=11 (binary) is output if R1<(input; y_(i)),

OUTPUT=10 (binary) is output if R2<(input; y_(i))≦R1,

OUTPUT=01 (binary) is output if R3<(input; y_(i))≦R2; and

OUTPUT=00 (binary) is output if (input; y_(i))≦R3.

Pattern Addition Circuit (FIGS. 11-13)!

FIG. 11 is a block diagram of the construction of the pattern additioncircuit 410 according to the embodiment. FIG. 12 is a top view of theoriginal glass table (platen) 203.

In FIG. 11, numeral 901 denotes a sub-scanning counter, numeral 902represents a main scanning counter, numeral 903 denotes a look-up tableRAM (hereinafter referred to as a "LUT"), numeral 904 denotes an ANDgate, numeral 905 denotes a flip flop, numerals 906, 907, 908, and 909denote registers, numeral 910 denotes a 4 to 1 selector, numerals 911and 913 denote AND gates, numeral 912 denotes an adder, and numeral 914denotes a binarization circuit which binarizes an image signal P whichhas been filtered by a spatial filter. The binarization circuit 914outputs "1" when a value of the image signal is greater than thepredetermined threshold, while the circuit 914 outputs "0" when thevalue is smaller than the predetermined threshold. The binary data whichis output from the circuit 914 is written in a dual port RAM 915.

The image to be written in the dual port RAM 915 is an image which hasbeen written in a particular place in the image scanner 201 such as 1201in FIG. 12. The image is placed on a component in the reader whichcannot easily be exchanged, i.e. at the outer side of the original glasstable (platen) 203 (a frame part supporting the glass plate) and theunder surface of the supporting frame within the area where the imagesensors of the carriage 226 can read that image.

When an image is written in the dual port RAM 915, the signal CNO is setto "0" (magenta recording scanning). It is controlled so that the imagesignal P is a signal derived from the green (G) signal of the CCD 210.This is because the green signal is the closest to the brightness signalof the image among the signals which can be easily produced.

The data stored in the dual port RAM 915 is read via a data bus Data andan address bus Adr by CPU 414.

Since the LUT 903 is also a dual port RAM, the CPU 414 writes the samedata as the one read out from the RAM 915 into the LUT 903.

The writing operation of the pattern to the LUT 903 (hereinafter, thisis referred to as a "service mode") is described with reference to theflowchart of FIG. 13. This is a mode which is only executed by a copymaintenance engineer once at the installation of the color copyingmachine. A reading operation of the pattern to be added to a specifieoriginal (writing operation of the pattern to the LUT 903) is performedwhen the service mode is on.

In the service mode, the CPU 414 sets the signal CNO to "0" (step S1501)and starts a pattern reading operation (step S1502). The CPU 414 sets aCPU address to the address of the dual port RAM 915 (step S1503) andreads the data out of the dual port RAM 915 (step S1504).

The CPU 414 then sets the CPU address to the address (A'11-A'0) of theLUT 903 (step S1505) and writes the data read out from the dual port RAM915 with respect to the LUT 903 (step S1506). The data is written viathe I/O-terminal D of the LUT 903.

The sub-scanning counter 901 counts the main scanning synchronizingsignal HSYNC while the main scanning counter 902 counts the signal CLK.Each counter repeatedly counts the signal in a cycle of a 9-bit width,that is, 512 cycles. As described above, the LUT 903 stores the patternsto be added and is supplied with the lower 6 bits (Q5-Q0) of each countvalue from the sub-scanning counter 901 and the main scanning counter902.

The AND gate 904 carries out the logical product (AND) between theoutput of the RAM 903 and each bit of an higher three bits (Q8-Q6) ofthe main scanning counter 901 and the sub-scanning counter 902 withreference to the 1 bit (D0). This logical product is synchronized withthe CLK signal by the flip flop 905. After the AND gate 913 carries outthe logical product between the 2-bit CNO0 signal (LSB side) and the2-bit CNO1 signal (MSB side), the result of the AND operation is outputto the AND gate 911. The value of the CNO0 signal is then inverted bythe inverter 916. This signal is effective only when CNO=2, that is,only when printing is being performed in yellow.

Values P1, P2, P3, and P4 are stored in advance in the registers 906,907, 908, and 909, respectively. One of the values P1-P4 is selectedaccording to the pattern level selection signal PS designated by the CPU414 and the value is supplied through the AND gate 911 to the adder 912where a pattern signal is added to an input signal V. The signalobtained by the adder 912 is output as a signal V'. Accordingly, in thecase of CNO=2, that is, printing in yellow is being performed, thepattern stored in the RAM 903 is repeatedly read out and added to thesignal to be output.

It should be noted that a relationship P1<P2<P3<P4 is established in P1,P2, P3 and P4. In the selector 910, the following relation is set:

Y=A is set when PS=00 (binary),

Y=B is set when PS=01 (binary),

Y=C is set when PS=10 (binary),

Y=D is set when PS=11 (binary).

Therefore, a pattern is added so that:

V'=V+P1 when PS=00 (binary),

V'=V+P2 when PS=01 (binary),

V'=V+P3 when PS=10 (binary),

V'=V+P4 when PS=11 (binary).

The adding pattern is formed only with a yellow toner so as to bedifficult to visually discriminate. This method is intended to utilizethe fact that the visual discriminating ability is weak with respect toa pattern formed with yellow toner. Furthermore, it is arranged that thelevel of the pattern to be added can be varied according to thepossibility of the existence of a specific original in the inputoriginal. It is thereby possible to make the pattern very difficult tovisually discriminate in ordinary copies. On the other hand, the patternis added more distinctly as the possibility of the existence of aspecific original increases.

Result of the Duplications (FIG. 14)!

FIG. 14 is a diagram showing an example of the result of duplicationsaccording to the first embodiment. In FIG. 14, an adding pattern isindicated by numeral 1001. The content stored in the LUT 903 is added.In the example shown in FIG. 14, the adding pattern which is "ABCD" and"1234" in the two rows is formed in 64×64 pixels such as to be difficultto visually discriminate. This pattern is repeatedly formed at intervalsof 512 pixels in the main scanning direction and at intervals of 512lines in the sub-scanning direction. If this adding pattern represents amanufacturer's serial number exclusively assigned to the copying machineor encoded pattern of this number, the machine used for copying can beidentified by examining the duplicates.

If there is a high possibility that a specific original which isprohibited from copying exists in the read image, a more distinguishablepattern can be added on the image in black toner.

In the first embodiment, the pattern adding pitch is predetermined as512 pixels in the main scanning direction and 512 lines in thesub-scanning direction. The patterns are therefore added at intervals ofapproximately 32.5 mm since the copying machine according to the firstembodiment has a resolution of 400 dpi (dots/inch). A bank note of theBank of Japan has a height of approximately 76 mm in the direction alongits short side. The short side of the paper money of major countries inthe world ranges from approximately 60 mm to 120 mm. The pattern cantherefore always be added when duplicating any bank note. Accordingly,if a part of the bank note forgery is cut out and used, the informationon the serial number of the copying machine used can be determined byexamining the part of the duplicate and reading the add on pattern.

Procedure of Setting the Pattern Level Selection Signal PS (FIG. 15)!

The procedure of setting the pattern level selection signal PS executedby the CPU 414 is described with reference to the flowchart of FIG. 15.

Immediately after the start of copying, at step S1102, "0" is set in thepattern level selection signal PS. At step S1103, the presentdetermination level H and the value of PS are compared. If H is greater,the value of H is set in PS at step S1104. If H is not greater, theprocess returns to step S1103. That is, the maximum value among thevalues from the copying start to the present time is set according tothe recording history of the determination signal H.

As described above, in the embodiment, a particular pattern which isdifficult to visually recognize is added in accordance with the degreeof the possibility of existence of a specific pattern, so that thepattern can be used as a key to identifying the copying machine in acase where a specific original (e.g. bank notes) which should not becopied is duplicated. The particular pattern is repeatedly added at apitch shorter than the height of the bank note in the direction alongthe short side thereof, so that the added particular pattern can alwaysbe included in a part of the copy of the bank note which may be cut outto use. It is possible to ascertain the copying machine used or it helpsinvestigate the person who might have operated the copying machine or,at least, reduce the number of suspected machines or persons byexamining the add-on pattern.

<Second Embodiment>

In the embodiment, as for addition of a predetermined pattern describedin the first embodiment, the case where it is controlled so that adensity of the predetermined pattern is changed in accordance with theposition of an original image to be duplicated, is described below.

FIG. 17 is a sectional view illustrating the construction of the mainportions of the full-color copying machine according to the embodiment.In FIG. 17, numeral 2001 is a polygon mirror, numeral 2002 is a mirror,numeral 2003Y is a yellow developing unit, numeral 2003M is a magentadeveloping unit, numeral 2003C is a cyan developing unit, numeral 2003BKis a black developing unit, numeral 2004 is a photosensitive drum,numeral 2006 is a recording paper, numeral 2007 is a fixing roller,numeral 2101 is an original image, numeral 2102 is an original glasstable (platen), numeral 2103 is a light source, numeral 2104 is anoptical lens, numeral 2105 is a CCD, and numeral 2106 is an A/Dconverter. Numeral 2012 is a shading circuit for performing a shadingcorrection of a digital signal obtained from the A/D converter 2106,numeral 2107 is a control circuit internally storing the CPUidentification number, numeral 2108 is a semiconductor laser, andnumeral 2116 is a power supply. Furthermore, numeral 2109 is anelectrostatic charger, numeral 2110 is a cleaning blade, numeral 2111 isa transfer drum, numeral 2112 is a transfer electrostatic charger, andnumeral 2113 is an ITOP generating circuit.

The color image formation sequence by the fullcolor copying machine withthe above arrangement is described below.

First, an image original 2101 placed on the platen 2102 reflects a lightirradiated from a light source 2103, the reflected light is collected bythe optical lens 2104, and an image is formed on a CCD 2105. The formedimage is then converted to an image signal corresponding to the amountof received light.

The image signal is converted to a digital value by the A/D converter2106 and the converted digital value is subject to the image processingin a control circuit 2107. Subsequently, the laser diode 2108 is drivenin accordance with the processed image signal (density signal).

A laser beam radiated by the semiconductor laser 2108 is reflected bythe polygon mirror 2001 and mirror 2002, and irradiated onto thephotosensitive drum 2004.

The surface of the photosensitive drum 2004 is cleaned by the cleaningblade 2110 so that toners will not contact in advance. Then, the surfaceof the photosensitive drum 2004 is equally electrified by theelectrostatic charger 2109 so as to be equipotential.

The photosensitive drum 2004 where a latent image is formed by scanningof the laser beam in accordance with the image signal Y (yellow) isrotated to the arrow's direction shown in FIG. 17, and an image isdeveloped by the developing unit 2003Y.

The photosensitive drum 2004 is further rotated and the recording paper2006 is drawn in and wound by the transfer drum 2111, and then a tonerimage formed on the photosensitive drum 2004 by the transferelectrostatic charger 2112 is transferred to the recording paper 2006.

Subsequently, a similar latent image formation is performed by using theimage signal of M, and the M image is multi-transferred onto therecording paper 2006, at the registration of the image, where the Yimage has already been transferred.

Similarly, the image formation and multi-transfer are performed inaccordance with the image signals of C and BK. Subsequently, therecording paper 2006 is removed from the transfer drum 2111 and carriedto the fixing roller 2007, and the image is fixed, thus a color imageprinting is completed.

FIG. 18 is a block diagram illustrating the construction of the controlcircuit 2107 of the fullcolor copying machine in accordance with theembodiment. In FIG. 18, numeral 2013 is a LOG converter, numeral 2014 isa LUT (look up table), numeral 2015 is a serial-number patterngeneration circuit, numeral 2016 is a modulation amount controller,numeral 2017 is a comparator, numeral 2018 is a pulse-width modulator,and numeral 2019 is a LD driver.

The image processing of the image signal (brightness signal) obtained bythe CCD 2105 executed by the controller 2107 is described below.

First, an image signal (a brightness signal) obtained by the CCD 2105 isconverted to a digital brightness signal by the A/D converter 2106. Thedigital brightness signal is subject to the shading correction in theshading circuit 2012 and the sensitivity fluctuation of each CCD iscorrected. The corrected brightness signal is then input to the controlcircuit 2107.

In the control circuit 2107, the LOG converter 2013 converts thecorrected brightness signal to a density signal. The density signal isfurther converted by the LUT 2014 so that the γ characteristic of theprinter at the initial setting coincides with the original image densityand the output image.

On the other hand, the serial-number-pattern generating circuit 2015generates a pattern which is unique to each copying machine. Similar tothe first embodiment, in this embodiment, a gap signal representing theunique pattern shown in FIG. 19 is added to the image density signal-ofY (yellow) which serves as a least visually sensitive color. In theembodiment, as a unique pattern, a serial-number pattern (numericalpattern) as shown in FIG. 20 is used. Furthermore, in FIG. 19, a lateralaxis represents a distance from the edge of a recording paper.

This serial-number pattern is read, after the fullcolor image is formed,by observing via a 350 nm narrow band filter, which separates the yellowsignal. Accordingly, if counterfeits are made, the copying machine usedfor forgery can be identified. In the embodiment, the serial-numberpattern corresponds to a numerical pattern as shown in FIG. 20. It ispreferable to use an imperceptible pattern composed of numbers orcharacters.

Furthermore, in order to add this serial-number pattern, a modulationamount (which corresponds to "d" in FIG. 19) is determined by themodulation amount controller 2016 with reference to a reference signalindicating an image start position supplied from the ITOP generationcircuit 2113. The modulation amount is output to the comparator 2017where it is added to the read image signal.

The image signal including the serial-number pattern is modulated by apulse-width modulator 2018 so as to be a laser luminance period inproportion to the density signal and the modulated image signal istransmitted to the laser driver 2019. In this way, a tone image isformed by expressing a density as a variation of an area where toner iscontacted in accordance with the modulated image signal.

The modulation amount (d) of the image signal for adding theserial-number pattern is set by the modulation amount controller 2016 asshown in FIG. 21 depending on the add-on position of the recording paper2006.

The area where an image is formed (image formation effective area) isset so as to be within the recording paper as shown in FIG. 21. This isbecause the transfer drum 2004 becomes dirty and the inside of thecopying machine is eventually likewise dirtied, if the image formationeffective area is larger than the recording paper. Moreover, it ismeaningless to form an image which is larger than the recording paper.Hereinafter, the edge of the image formation effective area shown inFIG. 21 is referred to as an "image boundary".

When the relationship between the size of the recording paper and theimage formation effective area is considered, in a case where theserial-number pattern is added over the entire recording paper and theportion in which the value of image density signal is substantially 0exists on the boundary, fog appears in the image formation effectivearea because of the density gap between the serial-number pattern andthe margin of the recording paper. For example, if the density gapindicated by a dotted circle shown in FIG. 19 exists in the vicinity ofthe image boundary, fog appears outstanding.

Therefore, as shown in FIG. 21, the modulation amount controller 2016takes a timing based on the ITOP signal generated by the ITOP generationcircuit 2113, and sets the modulation amount (d) to 0 in the startposition (S₁) for writing an image. The modulation amount controller2016 performs control in a manner such that the further the writingposition is from the image boundary, the greater the modulation amountbecomes until the writing position reaches a predetermined distance fromthe image boundary.

According to the embodiment, since a full-color image is formed byprinting over the images formed by a plurality of color toners and anaddition of information which is unique to the full-color copyingmachine onto the image of a predetermined color is performed by changingthe modulation amount of the add-on pattern in accordance with thedistance from an image boundary, fog due to the pattern generated in theimage boundary area can be made imperceptible.

Furthermore, in the embodiment, the modulation amount of the add-onpattern is controlled only in the leading edge side in the transformingdirection of the recording paper. However, as shown in FIG. 22, thecontrol in the ending edge side can also be performed. According to FIG.22, the modulation amount goes toward "0" as approaching the leadingedge (S1) and the ending edge (S2) of the image formation effective areaof the recording paper. Accordingly, fog appeared by addition of theserial-number pattern can be made imperceptible in both edges of theimage formation effective area.

In addition, it can be arranged such that the modulation amount of theadd-on pattern in the right edge and left edge of the recording paper(both edges of the image formation effective area which areperpendicular to the transferring direction) is controlled.

For example, as shown in FIG. 23, instead of a detecting signal of theleading portion of a recording paper supplied from the ITOP generator2113, a BD signal supplied from the BD detector 2114 is input to thecontrol circuit 2107 and a latent image formation start position in themain scanning direction is detected by a laser beam, and the positionsof the right and left edges of the recording paper are predicted fromthe detected position. Subsequently, as shown in FIG. 24, the modulationamount on the right and left edges of the image is controlled. Accordingto FIG. 24, as approaching the left edge (S₃) and the right edge (S₄) ofthe image formation effective area of the recording paper, themodulation amount goes toward "0", thus the modulation amount at theleft edge and right edges (S₃, S₄) becomes "0". Accordingly, fogappearing due to addition of the serial-number pattern can be madeundistinctive in both edges (S₃, S₄) of the image formation effectivearea.

As shown in FIG. 25, the BD detector 2114 is placed in the vicinity ofthe mirror 2002 so that the laser beam radiated by the semiconductorlaser 2108 and reflected by the polygon mirror 2001 is reflected intothe BD detector 2114 before it scans the photosensitive drum 2004 via af-θ lens 2115.

Furthermore, the modulation amount of the add-on pattern can becontrolled in the leading edge (S₁), ending edge (S₂), left edge (S₃),and right edge (S₄) in the image formation effective area of a recordingpaper by combining all of the controls described above. In this case, asshown in FIG. 26, the control circuit 2107 controls the modulationamount of the four edges by inputting the signals respectively suppliedfrom the ITOP generation circuit 2113 and BD detector 2114. Accordingly,fog appeared by addition of the serial-number pattern can be madeindistinctire in the four edges (S₁, S₂, S₃, S₄) of the image formationeffective area.

In each of the foregoing embodiments, the electrophotographic processfull-color copying machine is used as a typical image processingapparatus. However, this does not impose a limitation upon theinvention, for the invention is applicable to an ink-jet printer, athermal printer, or a bubble-jet printer employing a head of the typewhich jets droplets by utilizing film-boiling that relies upon thermalenergy.

In each of the foregoing embodiments, the patterns are added in yellow.However, this does not impose a limitation upon the invention, as thecolor can be replaced by a neutral tint such as yellow green and gray ora brighter color such as light purple and light green.

Furthermore, in each of the foregoing embodiments, the image of anoriginal is input by the scanning section. However, this does not imposea limitation upon the invention, for it is permissible to input an imageentered by a still-video camera or an ordinary video camera, as well asan image produced by computer graphics.

<Third Embodiment>

In the first embodiment and second embodiment, the resolution of eachcolor component is the same in the full-color image formationprocessing. However, in the third embodiment, the following case isdescribed: The resolution of the color component of the serial-numberpattern (which is yellow in the embodiment) is changed and the toneconversion characteristic of the color component of the serial-numberpattern to be added is made different from those of the other colorcomponents.

FIG. 27 is a general side view illustrating the internal construction ofa full-color copying machine in accordance with the embodiment. Theportions which are identical to those of FIG. 17 have the same referencenumerals and a redescription is not needed. Here, the portions havingunique characteristics of this embodiment are described. In thefull-color copying machine of the embodiment, a copy mode of theoperational panel (not shown) is switched between the character modeused when characters and line images are dominant in an image originaland the photo mode used when a tone image such as a photograph isreproduced.

In FIG. 27, numeral 2117 is a resolution switcher which switches arecording density depending on a color component. In the embodiment, inthe photo mode, it is set to 200 dpi of the recording density. In thecharacter mode, it is set to 200 dpi on Y (yellow) and 400 dpi on M(magenta), C (cyan), and BK (black).

The character mode where characters and line images are reproduced isdescribed with reference to the flowchart of FIG. 28.

When the copy start button (not shown) on the operation panel (notshown) is pressed, a recording paper 2006 is fed from a cassette (notshown) and wound by the transfer drum 2111 (step S21).

In the image formation process in each color component, first, a latentimage is formed on the Y component at the resolution of 200 dpi and thelatent image is visualized by the yellow developing unit 2003Y (stepsS22 and S23). Then, the formed yellow-toner image is transferred to therecording paper 2006 (step S24). Subsequently, an image formation isperformed on the M component at the resolution of 400 dpi, and then, themagenta-toner image is multi-transferred to the recording paper 2006where the yellow-toner image has been transferred in register (stepsS25-S27).

Similarly, the image formation and multi-transfer is performed on the Ccomponent and BK component. Subsequently, the recording paper 2006 isremoved from the transfer drum 2111 (step S34) and transferred to thefixing roller 2007 and the transfer image is fixed (step S35), thus aduplication of the full-color image is completed.

FIG. 29 is a four-quadrant chart showing how the density of an imageinput at the character mode is reproduced. Note that the tone isexpressed by an 8-bit digital signal, and therefore, there are 256(0-255) tones.

In FIG. 29, the quadrant I shows the characteristic of the image scannerfor converting an original density to a density signal (Signal 1) andthe quadrant II shows a LUT for converting the density signal (Signal 1)to a laser output signal (Signal 2). The quadrant III represents aconversion table from the laser output signal (Signal 2) to an outputdensity. It is set so that the output density (d_(out)) will not changemuch in an area where the signal value of the laser output signal issmall with respect to the change (d_(in)) of the laser output signal,while the output density is greatly changed in an area where the signalvalue of the laser output signal is large and the change of the laseroutput signal is small. This is set, considering the characteristics ofthe printer in the image output at the resolution of 400 dpi where thecharacter reproducibitity is high. Accordingly, it is controlled so thattoner will not be discharged in the highlight portion of the outputimage, while the toner will be sufficiently discharged in theintermediate to the high density portion.

Furthermore, in the LUT of quadrant II, the input/output relationship isset to be linear so that the characteristic of tone conversion of thedensity of an input image and the density of output image shown in thequadrant IV becomes S-shaped. Thus, a sharp and clear image in whichcharacters and line images are emphasized can be output.

The full-color image is formed via the above process. However, when atone image such as a photograph is duplicated, the copy mode is switchedto the photo mode.

FIG. 30 is a four-quadrant chart indicating the tone reproduction of theinput image in the photo mode. The number of the tones to be expressedis 256 (0-255).

In FIG. 30, the conversion relationship in each of the quadrants I-IV issimilar to that of FIG. 29. However, the conversion relationship fromthe laser output signal (Signal 2) to the output density in the quadrantIII is almost linear, and thus, the tone image is accurately reproduced.Furthermore, in the photo mode, the resolution of the full-color copyingmachine is 200 dpi.

In this embodiment, the serial-number pattern (See FIG. 20) which is thesame as that used in the second embodiment is also added on theduplication image. However, it goes without saying that, in addition tothe serial-number pattern of FIG. 20, the add-on image pattern can be apattern obtained by encoding dots which, at a glance, appear to bemeaningless.

In the embodiment, when a yellow image is formed, a small density value(d_(in)) representing a serial-number pattern is added to the densitysignal. This serial-number pattern can be read by observation via a bluefilter after the full-color image has been formed.

FIG. 31 is a four-quadrant chart showing the tone reproduction of yellowwhich is a color of the serial-number pattern added at the resolution of200 dpi. Since the serial-number pattern is added at the resolution of200 dpi, the image density change is small with respect to theenvironmental change and toner density change in comparison with theresolution of 400 dpi, thus, resulting in a stable output.

When a small density value (d_(in))is added to the laser output signal(Signal 2) based on the density of an input image, in a case with thetone conversion characteristic shown in FIG. 29, the density value(d_(in)) is not significantly reflected to the output image so much.Accordingly, an image having a yellow dominant background is output in amanner such that the density value (d_(in)) of an output image ismaintained in the output of the Y component, even if the value is small,and the conversion characteristic from a density signal (Signal 1) to alaser output signal (Signal 2) in the quadrant II is set to benon-linear, as shown in FIG. 31. Thus, the conversion result in thequadrant IV becomes the same as the output characteristic of the othercolor components when the small density value is added to the laseroutput signal (Signal 2). Accordingly, the density representing aserial-number pattern can be fully expressed on an output image bymodifying the LUT representing the conversion characteristic from thedensity signal (Signal 1) to the laser output signal (Signal 2).

Furthermore, a desirable conversion characteristic from the laser outputsignal to the density of an output image can be obtained by changing thedeveloping bias by using a generally well-known cause and effectrelationship between the developing bias applied to the developing unitand the conversion relationship between the laser output signal (Signal2) and the density of an output image.

FIG. 32 is a diagram illustrating an example of a developing bias of aregular rectangular wave. FIG. 33 is a diagram illustrating theconversion characteristic of the laser output signal (Signal 2)corresponding to the developing bias shown in FIG. 32 and the density ofthe output image. However, in the conversion characteristic shown inFIG. 33, in the highlight portion (where the intensity of the laseroutput signal is small) and the high density portion (where theintensity of the laser output signal is large), even if the smalldensity value (d_(in)) representing the serial-number pattern is added,the serial-number pattern will not be outstanding on the output imageand will not be read by the image reader. On the other hand, in theintermediate density portion (where the intensity of the laser outputsignal is intermediate), if the small density value (d_(in))representing the serial-number pattern is added, the serial-numberpattern will be outstanding on the output image because it appears as alarge density change in the output image.

Accordingly, the developing bias waveform is changed as shown in FIG. 34and the conversion characteristic between the laser output signal(Signal 2) and the density of the output image becomes substantiallylinear so that the addition of the small density value (d_(in))representing the serial-number pattern appears equally in all densityvalues of the output image and the pattern is made indistinctive.

In the character mode, on the M, C, BK components, an image formationusing the conversion characteristic shown in FIG. 33 is performed. Onthe Y component, an image formation using the conversion characteristicshown in FIG. 35 is performed.

Alternatively, the conversion characteristic of the laser output signal(Signal 2) and the density of an output image is controlled so as to besubstantially linear by not changing the developing bias applied to thedeveloping unit, but by adjusting the surface electric-potential of thephotosensitive drum 2004.

FIG. 36 is a diagram illustrating the surface electric-potential of thephotosensitive drum 2004 in accordance with the intensity of the laserbeam depending on the laser output signal (Signal 2). In FIG. 36, V_(FF)refers to a surface electric-potential when the density value is "255",V₀₀ refers to a surface electric-potential when the density value is"0", and V_(DC) refers to a developing electric-potential.

In general, as the value of |V₀₀ -V_(DC) | gets larger, the toners havedifficulty staying in contact with the photosensitive drum. Theconversion characteristic of the laser output signal (Signal 2) to thedensity of the output image is a characteristic shown in FIG. 37. Inaddition to the characteristic such that the toner is difficult tocontact in the area where the density value is small (at a highlightportion), the density value of an output image is not changedsignificantly with respect to the laser output signal (Signal 2).Accordingly, when the density value representing the serial-numberpattern is added, the pattern will not be distinctive on the outputimage and cannot be read by the image reader. On the other hand, thereis a tendency such that toners readily adhere to the photosensitive drumas the value of |V₀₀ -V_(DC) | becomes small. The conversioncharacteristic of the laser output signal (Signal 2) to the density ofthe output image is substantially linear as shown in FIG. 38.Accordingly, the change of the laser output signal (Signal 2) accuratelyreflects on the density value of the output image over all the densityvalues. Therefore, if the small density (d_(in)) representing theserial-number pattern is added, it can be expressed on the output imageover all the density values.

According to the embodiment, the Y component of the serial-numberpattern to be added is set so as to be |V₀₀ -V_(DC) |=80 V, and theconversion characteristic of the laser output signal (signal 2) and thedensity of the output image shown in FIG. 38 is provided. On the otherhand, on the M, C, BK components, it is set so as to be |V₀₀ -V_(DC)|+150 V and the conversion characteristic shown in FIG. 37 is provided.Accordingly, a serial-number pattern can be properly added in thehighlight portion.

According to the embodiment, information which is unique to eachapparatus, that is, a serial-number pattern, is stably formed on aduplicated copy in a manner such that the tone characteristic of theparticular color (Y) which is used to form the serial-number pattern ismade different from those of the other colors and the density valuerepresenting the serial-number pattern is constantly preservedregardless of the density value of the output image.

In the foregoing embodiment, in the character mode in particular, theimage output of Y is performed at the resolution of 200 dpi, however,this does not impose a limitation upon the invention. For example, theimage output resolution of Y can be set to the same resolution of theother color components in order to improve the character reproduction.

<Fourth Embodiment>

In this embodiment, the following case is described: Particularinformation is expressed by combining a plurality of predeterminedpatterns which are added to the Y component by using the full-colorcopying machine with the arrangement indicated by FIG. 1 and theplurality of patterns in the main scanning direction and sub-scanningdirection of the output image are output periodically.

Image Scanner (FIG. 39)!

FIG. 39 is a block diagram illustrating the construction of the imagescanner 201. In FIG. 39, the portions which are identical to those inFIG. 2 have the same reference numerals and a redescription is notneeded.

In the embodiment, the density conversion circuit 408 may be controlledso as to select one of the ROMs storing a plurality of tonecharacteristics in accordance with the frame-sequential signal, thesignal CNO (refer to FIG. 16) which is described in the firstembodiment. Furthermore, it can be controlled so that the tonecharacteristic of density conversion data which is stored into the RAMis modified by the CPU 414.

The signal CNO which is respectively input to the masking/UCR circuit406 and pattern addition circuit 410 is generated via the CPU 414 andI/O port 413, and the operational condition of the masking/UCR circuit406 and pattern addition circuit 410 is switched in accordance with thevalue of the signal CNO.

Pattern Addition Method!

FIG. 40 is a diagram for describing an example of the add-on pattern inaccordance with the embodiment.

In FIG. 40, 4×4 pixels included in the area 1301 is modulated so thatthe tone of the image signal is to be +α and the 2×4 pixels included inthe areas 1302 and 1303, respectively, are modulated so that the tone ofeach image signal is to be -a. The pixels outside of the areas 1301-1303are not modulated. The 8×4 pixels included in the areas 1301-1303 arereferred to as a "unit dot of an add-on pattern" (hereinafter, referredto as a "unit dot"). The reason why 8×4 pixels are used for a unit ofthe add-on pattern is because there may be a case where the add-onpattern is difficult to be read, if a unit of the adding pattern is setto one pixel.

FIGS. 41 and 42 are diagrams illustrating the construction of a linewhere the pattern is added (hereinafter, referred to as an "add-online").

In FIG. 41, numeral 1401 is an add-on line having a width of 4 pixels,numerals 1401a-1401e are unit dots, each of which consists of 8×4pixels. These unit dots are arranged in a predetermined interval (i.e.128 pixels) in the main scanning direction.

In FIG. 42, numerals 1501-1510 are add-on lines having a width of 4pixels and arranged in a predetermined cycle d2 (i.e. 16 lines) in thesubscanning direction. For example, a single add-on line represents4-bit information and eight add-on lines 1502-1509 can represent 32-bitadditional information. The add-on lines are repeatedly formed in thesubscanning direction, for example, the information of the add-on line1501 is identical to that of the add-on line 1509. The details will bedescribed later.

FIGS. 43, 44A, and 44B are diagrams illustrating the informationrepresentation method by the add-on lines.

FIG. 43, numerals 1601 and 1602 are add-on lines which are next to eachother in the sub-scanning direction in the interval of d2. Numerals1601a, 1601b, and 1602a are unit dots. In order to prevent the unit dotswhich are next to each other from being outstanding, each of these unitdots is located in an interval d3 (i.e. 32 pixels) in the main scanningdirection.

The data represented by the unit dot is determined by the phasedifference between the unit dot 1602a and unit dot 1601a. FIG. 43 showsan example representing 4-bit information (information in which the datavalue is one of 0-F (in terms of hexadecimal representation)). In FIG.43, the unit dot 1602a represents data value "2"For example, if the unitdot 1602a is located at the left end, the data value is "0", while if itis at the right end, the data value is "F".

FIGS. 44A and 44B illustrate a set of add-on lines representing alladditional information (32 bits). FIG. 44A shows a first add-on line"line 0" and FIG. 44B shows a fourth add-on line "line 3".

As shown in FIGS. 44A and 44B, in Line 0, the dots 1702a-1702d arerespectively added to the right-side of the unit dots 1701a-1701d withan interval d4 (e.g. 16 pixels). In "line 3", the dots 1705a-1705d arerespectively added to the right side of the unit dots 1704a-1704d withan interval d5 (e.g. 32 pixels). These additional dots 1702a-1702d and1705a-1705d are markers for clarifying each add-on line's location.Hereinafter, this additional dot marker is referred to as a "marker".The reason why the marker is added to two add-on lines is to define thetop and bottom in the sub-scanning direction from the output image.

Furthermore, the add-on pattern is added only in yellow toner byutilizing the fact that the human eye is visually insensitive to apattern printed in yellow.

Still further, a dot interval in the main scanning direction of theadd-on pattern in an objective specific original and a repeatinginterval of all additional information in the sub-scanning directionneeds to be determined so that the dots comprising the add-on patterncan be identified and all the information can accurately be added. As astandard, the information can be added at a pitch equal to/less thanhalf the width or the height of the objective specific original.

Pattern addition Circuit!

FIGS. 45-47 are block diagrams illustrating the construction of thepattern addition circuit 410. In FIGS. 45-47, a sub-scanning counter 819and main scanning counter 814 respectively count main scanningsynchronizing signal HSYNC and the signal CLK repeatedly in 7-bit width(each of the bits is referred to as Q6, Q5, . . . , Q0), that is, in acycle of 128 signal pulses. An AND gate 820 connected to bit Q2 and bitQ3 of the sub-scanning counter 819 outputs "H" when each of the bit Q2and bit Q3 is "H". That is, the output of the AND gate 820 is "H" forfour lines every 16 lines in the sub-scanning direction and this is usedas an enable signal of the add-on line.

A gate 822 generates an enable signal "line 0" of the add-on line "line0" with the input of the three higher order address bits (Q4-Q6) of theoutput of the AND gate 820 and that of the sub-scanning counter 819.Similarly, a gate 821 generates an enable signal LINE 3 of the add-on"line 3".

On the other hand, an initial value is loaded to the main scanningcounter 814 by the HSYNC and the gates 815-817 input four higher orderaddress bits (Q3-Q6) of the main scanning counter 814. The output of theAND gate 815 becomes an 8-bit interval "H" in every 128 pixels in themain scanning direction, and this is used as an enable signal of a unitdot. Furthermore, the gates 816 and 817 respectively input the linesignals "line 0" and "line 3" in addition to the four higher addressbits of the main scanning counter 814, and generate enable signals asmarkers of Line 0 and Line 3. The unit dots and enable signals of themarkers are integrated into one in an OR gate 818. An AND gate 824carries out a logical AND between the output of the OR gate 818 and theoutput of the OR gate 820. It is an enable signal of the unit dot andmarker, each of which is "H" on the add-on line.

The output of the AND gate 824 is synchronized with the signal CLK in aflip flop F/F 828 and an AND gate 830 carries out a logical AND betweenthe output of the AND gate 824 and a 2-bit output color selection signal(frame-sequential signal) CNO. The bit 0 of the output color selectionsignal CNO is inverted by the inverter 829 and the inverted value isinput into an AND gate 830. Since the bit 1 of the output colorselection signal CNO (CNO 1) is input into the AND gate 830 as is, theenable signal becomes effective when the output color selection signalCNO is "2", that is, when the image of the Y component is formed.

The output of the AND gate 824 is also supplied to a clear terminal CLRof a counter 825. The counter 825 counts the signal CLK only when theoutput of the AND gate 824 is "H", that is, the output of the unit dotof the add-on line is enabled. The bit 1 (Q1) and bit 2 (Q2) of theoutput of the counter 825 are input to an EXNOR gate 826 and the outputof the EXNOR gate 826 becomes "L"for four pulses of the signal CLK whichcorresponds to a half of the dots of the add-on line (for 8 pulses ofthe signal CLR). The output of the EXNOR gate 826 is synchronized withthe signal CLK by the flip flop F/F 827 and output as a signal MINUS.

When the MINUS signal is "L", the unit dot of the add-on line ismodulated to +α. The flip flop F/F serves as a phase adjuster so thatthe phase of the signal MINUS coincides with that of the output of theenable signal of the unit dot. The signal MINUS is input to a selectionterminal S of a selector 838.

The AND circuit 832 is supplied with an 8-bit modulation amount α fromthe resister 831 and the output of the AND gate 830. When the timingwhen a unit dot of the add-on line is output, the output of the AND gate830 is "H". Thus, the modulation amount α is output from the AND circuit832 at the timing when the unit dot of the add-on line is output.Accordingly, in a pixel other than the unit dots of the add-on line, theoutput of the AND circuit 832 is "0", therefore, the modulation will notwork.

In FIG. 45, numeral 833 is an adder, numeral 835 is a subtracter. Theterminal A in each of the adder 833 and subtracter 835 is supplied withan 8-bit image signal V from the density conversion circuit 408. Theterminal B in each of the adder 833 and subtracter 835 is supplied witha modulation amount α which is output from the AND circuit 832. Theaddition result (V+α) output from the output terminal (A+B) of the adder833 is input to an OR circuit 834, while the subtraction result (V-α)output from the output terminal (A-B) of the subtracter 835 is input tothe AND circuit 837.

In the OR circuit 834, when the addition result (V+α) has an overflowand a carry signal CY is output, the value of the operational result isautomatically set to "255". On the other hand, in the AND circuit 837,when the subtraction result (V-α) has an underflow and a carry signal CYis output, the value of the operational result is automatically set to"0" by the inverted carry signal CY by the inverter 836. Bothoperational results (V+α) and (V-α) are input to the selector 838 and asignal V' is output from the selector 838 in accordance with the signalMINUS.

Accordingly, the dot modulation is performed on the 8-bit image signal Vwhich is input from the density conversion circuit 408.

The value which is loaded to the main scanning counter 814 is generatedas described below.

Since the flip flop F/F 863 and main scanning counter 809 are reset bythe sub-scanning synchronizing signal VSYNC, the initial value of themain scanning counter 814 is set to "0" in a first add-on line.

The selector 860 selects one of registers 851-858 where a 4-bit value ofthe 8 add-on lines is set in accordance with a 3-bit signal (selectsignal) input to the select terminal S and the value corresponding tothe selected register is output.

The select signal of the selector 860 is generated by the counter 859which counts signal ADLIN. Since the counter 859 is cleared by thesub-scanning synchronizing signal VSYNC at the first add-on line timing,the selection signal is "0". Accordingly, the selector 860 selects theregister 851. When the signal ADLIN is provided, the count value of thecounter 859 is increased by one and the selector 860 selects theregister 852. Subsequently, the selector 860 is synchronized with thesignal ADLIN and selection of the registers 853-858 is sequentiallyrepeated.

The output of the selector 860 is input to the adder 861 and added tothe output of the adder 862. The addition result is input to a flip flopF/F 863 and latched at the fall of the signal ADLIN (the timing when thesignal value is changed from "H" to "L"). The result is input to themain scanning counter 814.

The output of the flip flop F/F 863 is also supplied to the inputterminal B of the adder 862 and is added to a predetermined value, e.g.8, which is input to the input terminal A of the adder 862. Thispredetermined value is an off-set value to have an interval between theunit dot position of the add-on line and the dot position of the add-online of the preceding line in the sub-scanning direction.

The Result of Duplication!

The result of duplication where the pattern is added on the image isshown in FIG. 48. In FIG. 48, numeral 1901 is a specific original image.The unit dot of the add-on line is denoted by a black square. FIG. 48shows the arrangement of the unit dots of the add-on line in particular.

According to the embodiment, since the serial number which is unique tothe full-color copying machine or the encoded pattern of the serialnumber is expressed by a plurality of add-on patterns and the pattern isadded on a duplication image periodically, when the full-color copyingmachine of the embodiment is used for forgery of bank notes orsecurities, the machine used for the forgery can be identified from theinvestigation of the duplication.

In the embodiment, when the pattern is added on an input image, themodulation amount of the add-on pattern is input from the registerprovided in the pattern addition circuit 410, however, this does notimpose a limitation upon the invention. For example, as shown in FIG.49, it can be arranged such that the modulation value controllingcircuit 1413 detects a density value of the 8-bit image signal V inputfrom the density conversion circuit 408, controls a modulation amount αof the add-on pattern in accordance with the detected density value, andsets the modulation amount in the register of the pattern additioncircuit 410. In this case, the construction of the pattern additioncircuit 410 is as shown in FIG. 50. In FIG. 50, the modulation amount αoutput from the modulation controlling circuit 1413 is set in theregister 831.

According to the above-described arrangement, the pattern can be addedin a manner such that the modulation amount α is increased for the imagehaving a low density in accordance with the density value of the 8-bitimage signal V input from the density conversion circuit 408.

When the pattern is added to an output image, deterioration of the imagequality relative to the addition of the pattern can be suppressed in amanner such that complementary image signal modulations are combined ina small area in the vicinity of the position where the pattern is addedand the overall density is preserved, thus eliminating the change oftones. Furthermore, the complementary image signal modulation isadvantageous since when the output image is microscopically seen, theadd-on pattern can be easily read and the additional information can beread accurately.

<Fifth Embodiment>

In this embodiment, the case where the serial-number pattern shown inFIG. 20 is added while changing the density of a duplication image byusing the control circuit 2107 having the same construction as thefullcolor copying machine described in the second embodiment. Theaddition is performed only on the image signal of yellow, the color towhich the human eye is least sensitive.

The color image formation procedure according to the embodiment isdescribed with reference to the flowchart shown in FIG. 51.

The photosensitive drum 2004 where a latent image is formed by scanningof the laser beam radiated based on the image signal of the Y componentis rotated to the arrow's direction of FIG. 17, and the yellowdeveloping unit 2003Y performs a developing operation on the Ycomponent. The photosensitive drum 2004 is further rotated and arecording paper 2006 is sucked and attached by the transfer drum 2111(step S91), and then, a yellow toner image formed on the photosensitivedrum 2004 by the transfer electrostatic charger 2112 is transferred(step S92).

Subsequently, a latent image formation and development are performedbased on the image signal of the M component, an M toner image ismulti-transferred on the Y toner image on the recording paper 2006 inregister (step S93). Similarly, the image formation and multi-transferare performed based on the image signals of C and BK components (stepsS94 and S95).

Then, the recording paper 2006 on which the image transfer has beencompleted is separated from the transfer drum 2111 (step S96), and therecording paper 2006 is transferred to the fixing roller 2007 and thetransferred image is fixed (step S97). Accordingly, the color imageduplication is completed.

The adding processing of the output image and serial-number pattern inaccordance with the embodiment is described with reference to FIGS.52-54.

FIG. 52 is a diagram illustrating the relationship between the densitydistribution of the image with respect to an arbitrary direction on theduplicate image by the full-color copying machine and the density valueof the serial-number pattern which is added on the image.

The serial-number pattern generation circuit 2015 (See FIG. 27)generates a serial-number pattern as shown in FIG. 20 to specify thecopying machine. However, in the embodiment, the serial-number patterngenerated in the serial-number pattern generation circuit 2015 ischanged in accordance with the density value of the image, to which agap signal representing the density of the pattern is added by themodulation amount controlling circuit 2016. For example, in the case ofFIG. 52, it is arranged so that the density signal (d₁) of a gap signalis large when the density value of the add-on image is small, while thedensity signal (d₂) is small when the density value of the add-on imageis large. The relationship between the density value of an image and thedensity value representing a serial-number pattern to be added isspecifically described later with reference to FIGS. 53, 54A, and 54B.

Similar to the second embodiment, the serial-number pattern modulated inthis way is added to the input image signal by the comparator 2017.

FIG. 53 is a four-quadrant chart which is similar to FIG. 29. Themeaning of each quadrant and input signals, and the number of tones ofthe output image signal in FIG. 53 are the same as those in FIG. 29.

It is well-known that the conversion characteristic of the laser outputsignal (Signal 2) and the density of an output image in the quadrant IIIcan be in various forms due to the condition of a photoreceptor, laserspot diameter, and characteristic of development. In general, thecharacteristic is an S-shaped characteristic as shown in FIG. 53. On theother hand, in order to accurately reproduce a full-color image inaccordance with the density of the input image, it is important that therelationship between the density of an input original image and that ofthe output image in the quadrant IV be linear. To do so, the conversioncharacteristic in the quadrant III needs to be S-shaped as shown in FIG.53.

In the embodiment, the modulation signal of the serial-number pattern isadded to the laser output signal (Signal 2) obtained from the density ofthe input image. This add-on amount (d) is represented by d_(in) on theaxis of the laser output signal (Signal 2). In other words, the d_(in)is added to the laser output signal (Signal 2). As shown in FIG. 53, thevalue d_(in) is changed so that the value (d_(out)) after the conversionbecomes constant regardless of the density of the output image.

The above description is summarized in FIGS. 54A and 54B. The modulationpattern which is added to the laser output signal (Signal 2) shown inFIG. 54A has a modulation characteristic so as to be modulated as shownin FIG. 54B in accordance with the density value of the output image.The notation A on the vertical axis in FIG. 54B denotes a modulationamount. As shown in FIG. 54B, since there is no substantial meaning inthe area which is close to the maximum density (255) on the modulationto the positive side, it is set so that the modulation amount (Δ) is "0"at the maximum density.

In this way, the reproducibility of the serial-number pattern isimproved in the highlight portion (where the density value is small),while the pattern will not be distinctive in the intermediate range in amanner such that the modulation amount (d_(out)) representing theserial-number pattern in the output image is maintained to be constant.

According to the embodiment, a full-color image is formed by adding theimages formed by using a plurality of toners. When the serial-numberpattern which is unique information is added to the image in aparticular color such as yellow, the modulation amount of the add-onpattern is changed in accordance with the density of the image densitysignal, and thus, the unique information can be properly output on theoutput image regardless of the density of the output image.

In the embodiment, it is arranged so that the serial-number pattern caneasily be recognized in the highlight portion by modulating to thepositive side. However, this does not impose a limitation upon theinvention. For example, it can also be arranged so that theserial-number pattern can easily be recognized in the intermediate tothe high density range by modulating to the negative side. In this case,the modulation pattern and the modulation characteristic arerespectively shown in FIGS. 55A and 55B. Accordingly, the serial-numberpattern in the intermediate density range to the high density range caneasily be recognized.

Furthermore, the serial-number pattern can easily be recognized over allthe density values by combining the above two modulations and performingthe modulation at both the positive side and negative side.

In this case, the modulation pattern and the modulation characteristicare respectively shown in FIGS. 56A and 56B. By virtue of themodulation, the serial-number pattern can easily be recognized over allthe density values.

Still further, in the above embodiments, the fullcolor copying machineis described as an example, however, this does not impose a limitationupon the invention. The present invention can also be applied toprinters and printer interfaces without departing from the spirit andscope thereof. It should be noted that the specific original includesnot only bank notes and securities which are prohibited from beingcopied by law, but also confidential documents for a particular use.

The present invention can be applied to a system constituted by aplurality of devices, or to a machine comprising a single device.Furthermore, it goes without saying that the invention is alsoapplicable to a case where the object of the invention is attained bysupplying a program to a system or apparatus.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

Also, it goes without saying that the apparatus can be arranged bycombining the spirit and scope of each embodiment.

What is claimed is:
 1. An image processing method for supplying imagedata to an image forming apparatus capable of forming an image in aplurality of resolutions, comprising:input step of inputting image datarepresenting an image; and adding step of adding a predeterminedinformation on the image represented by the image data, wherein saidadding step adds the predetermined information in a lower resolution. 2.An image processing apparatus for forming apparatus capable of formingan image in a plurality of resolutions, comprising:input means forinputting image data representing an image; and adding means for addinga predetermined information on the image represented by the image data,wherein said adding means adds the predetermined information in a lowerresolution.
 3. The image processing apparatus according to claim 2,wherein one of the plurality of resolutions is selected in accordancewith a process mode.
 4. The image processing apparatus according toclaim 3, wherein a higher resolution is selected when a character modeis set.
 5. The image processing apparatus according to claim 4, whereinthe character mode is set, using an operational panel.
 6. The imageprocessing apparatus according to claim 2, wherein the predeterminedinformation is information for specifying the image processingapparatus.
 7. The image processing apparatus according to claim 6,wherein the information is provided by a supplier who supplies the imageprocessing apparatus.
 8. The image processing apparatus according toclaim 7, wherein the information is a manufacturer's serial number. 9.The image processing apparatus according to claim 2, wherein thepredetermined information is added so as to be difficult to visuallydiscriminate.
 10. The image processing apparatus according to claim 2,wherein the predetermined information is added to a yellow component ofthe image data.
 11. A color image processing method of adding apredetermined pattern on an input image comprising:an input step ofinputting a plurality of color component image data representing a colorimage; a conversion step of converting each color component image datainto output density data; and an adding step of adding the predeterminedpattern on the output density data corresponding to one of the pluralityof color component image data in such a manner that the added densityvalue representing the predetermined pattern is constant over any valueof the output density data, wherein a conversion characteristic of saidconversion step with respect to the color component on which thepredetermined pattern is added differs from that with respect to thecolor component on which the predetermined pattern is not added.
 12. Acolor image processing apparatus capable of adding a predeterminedpattern on an input image comprising:input means for inputting aplurality of color component image data representing a color image;conversion means for converting each color component image data intooutput density data; and adding means for adding the predeterminedpattern on the output density data corresponding to one of the pluralityof color component image data, whereina conversion characteristic ofsaid conversion means with respect to the color component on which thepredetermined pattern is added differs from that with respect to thecolor component on which the predetermined pattern is not added, and anadded amount of the density representing the predetermined pattern isconstant over any value of the output density data in a color componentthat the predetermined pattern is added.
 13. The color image processingapparatus according to claim 12, wherein an input/output conversioncharacteristic between the input color image data of a color componenton which the predetermined pattern is not added and the output densitydata obtained in a manner that the input color image data of the colorcomponent is converted by said conversion means is the same as thatbetween the input color image data of a color component on which thepredetermined pattern is added and the output density data obtained in amanner that the input color image data of the color component isconverted by said conversion means and added on the predeterminedpattern by said adding means.
 14. The color image processing apparatusaccording to claim 12, further comprisingimage formation means forforming a color image based on the output density data obtained by saidconversion means or output density data on which the predeterminedpattern is added by said adding means.
 15. The color image processingapparatus according to claim 14, wherein the color image formation isperformed in accordance with the electrophotographic process such that alatent image is formed by scanning a photosensitive drum, which iselectrified, by a laser beam to be equipotential and the latent image isdeveloped, andthe conversion characteristic of said conversion meansdepends on, at least, the intensity of the laser beam, a developing biaswaveform which is applied to a developing unit where the developing isperformed, a developing bias electric potential, an electrificationelectric potential of the photosensitive drum, and the relationshipbetween the intensity of the laser beam and the output density value.16. The color image processing apparatus according to claim 12, whereinthe plurality of color components representing the output density dataare yellow, magenta, cyan, black, and the color component for adding thepredetermined pattern is yellow.